The invention relates to a rack for electronic plug-in units, comprising a backplane, which comprises at least one connector to which a connector provided in the electronic plug-in unit connects when the plug-in unit is pushed into the rack.
A rack means a box-like frame into which electronic plug-in units are pushed. The structure can be hierarchical, i.e. the plug-in units can be placed directly in the rack, or alternatively the rack can be provided with subracks in which the plug-in units are placed. In one feasible structure the rack is divided into several compartments by shelves, which support either the plug-in units or the subracks. Since this structure is not relevant to the present invention, in this application the term rack refers to a mechanical structure consisting of one or more entities into which electronic plug-in units are pushed. Racks usually have standard measures, e.g. as described in Finnish standard SFS 2667 Elektroniikkalaitteiden kehikko-ja telinerakenteiden mitoitus (Dimensions of frame and rack structures in electronic devices) published by the Finnish Standards Association, which is incorporated herein by reference. Commercially available racks are usually dimensioned in inches.
A rack can be also protected by placing it in a cabinet. A typical example of a rack placed in a cabinet is a base station or a switching centre. When a rack is placed in open air, the cabinet protects the sensitive electronics from changes in temperature and humidity. The cabinet may also be provided with heating/cooling devices to balance the temperature and humidity. In that case the plug-in units include the electronics of a base station, e.g. transceivers.
A backplane is an essential part of the rack. The backplane comprises inter-board telecommunication routes, and/or telecommunication routes that connect the apparatus to the outside world, and/or the current supply connection. The backplane is usually implemented as a printed circuit board on which current and/or signals pass. The backplane is also known as a motherboard.
The plug-in unit refers to an electronic module which is installed in the rack. The plug-in unit comprises at least one connector which connects to the connector in the backplane when the plug-in unit is pushed into the rack. The connectors usually form a male/female connection. Usually the plug-in unit is provided with a male connector and the backplane with a female connector. The connectors may comprise guide surfaces and/or a pair of connectors may be provided with a pair consisting of a guide pin and a hole, which guide final connecting of the connectors. However, if the connectors are not sufficiently aligned, the guide surfaces do not help but the connector is damaged when the plug-in unit is pushed into the rack. Usually the plastic in the connector body breaks first, after which the connector pins may twist or break. On the other hand, the connector pair may remain undamaged but the attachment of the connector to the backplane or to the plug-in unit may be damaged, e.g. a soldered joint comes loose or a leg breaks. The backplane may also be damaged by inaccurate alignment. For example, a plug-in unit which contains a base station transceiver may weigh 15 kg. When such a heavy plug-in unit is pushed into a rack, one connector or both of the opposite connectors are damaged if they are unaligned. The weight of the plug-in unit is not, however, the only decisive factor but also the fact how fast the installation is carried out. Consequently, the connectors of units of all weights may be damaged upon installation. In practice one plug-in unit may include several connectors and they all may be damaged due to inaccurate alignment. The situation is made worse by the fact that the design of the racks does not usually allow one to see how well the connectors connect when a plug-in unit is pushed into the rack. The reason for this is that the rack may be against the wall and thus one does not have access behind it; on the other hand, the structure is usually enclosed, in which case this would be of no avail. Furthermore, the racks are usually next to one another and one cannot see through the backplane, which in practice makes manual and/or visual alignment of the connectors impossible during installation.
It is known to attach the backplane to the rack so that it cannot move. In that case the manufacture precision has to be very high so as to avoid damage to the connectors at the back of the rack when the plug-in unit is pushed into the rack. To achieve manufacture precision with a desired tolerance, it is possible to use a specific assembly jig where the rack and its backplane are assembled. The correct positioning of the connectors can be checked by using specific dummy plug-in units. The problem related to this solution is that it requires manual work. Furthermore, if a part of the rack or the backplane needs to be changed in field conditions at the final location of the rack, the alignment achieved with the assembly jig is lost. Parts may have to be changed because of damage to a part or when a new version of a part, particularly of the backplane, is introduced. Another problem related to rigid joint of this kind is that when the rack moves, e.g. due to vibration caused by an earthquake or traffic, the connectors may break. This results from the fact that the plug-in unit moves in relation to the backplane and/or the rack chassis. The plug-in units are usually attached to the front of the rack with screws and since they are attached rigidly to the back of the rack only with connectors, the forces generated by the movement of the rack break the connectors. Since in practice the plug-in unit and the backplane cannot be attached to each other so closely that they would function as one piece, they start to vibrate at different frequencies as the rack moves, as a result of which a connector, for example, breaks.
Another solution is to use specific floating connectors which enable blind mating. Blind mating refers to a situation where the alignment of the connectors cannot be seen directly. A floating connector is provided with a certain play in the direction perpendicular to the direction in which the plug-in unit is pushed, i.e. in principle in two directions: up and down in the directions of the x and the y axis and sideways but not in the direction of the z axis, i.e. in the depth direction. The problem associated with floating connectors is that they are expensive: they cost even 5 to 10 times as much as ordinary connectors because they include more parts, even a separate circuit board. Furthermore, the supply of floating connectors is smaller than that of ordinary connectors.
The object of the invention is to provide an improved rack. According to an aspect of the present invention, there is provided a rack for electronic plug-in units, comprising: a backplane, which comprises at least one connector to which a connector provided in the electronic plug-in unit connects when the plug-in unit is pushed into the rack; a fastener made of a resilient material for attaching the backplane to the rack so that the backplane can flexibly move in relation to the rack, there being a tolerance for alignment of the connectors enabling connection of the connectors when the plug-in unit is pushed into the rack, and when the plug-in unit is in the rack, the mobility of the backplane prevents the connectors and/or the backplane from breaking as the rack moves; and a moment arm formed between a point which attaches the fastener to the rack and the backplane.
The invention is based on the fact that a backplane is attached to a rack in such a manner that it can flexibly move in relation to the rack. When a plug-in unit is pushed into the rack, there is a tolerance for alignment of the connectors enabling connection of the connectors, and when the plug-in unit is in the rack, the mobility of the backplane prevents the connectors from breaking as the rack moves.
When the solution according to the invention is used, the apparatus does not need to be assembled using an assembly jig, which facilitates the manufacture of the apparatus as well as its maintenance in field conditions. However, the solution is mechanically so simple that it does not increase the production costs. Furthermore, the solution even enables inexpensive production of devices in accordance with Earthquake Zone 4 defined in the NEBS standard (NEBS=Network Equipmentxe2x88x92Building System) published by Bellcore.